Ulsan: Three researchers died of suffocation during vehicle testing at a Hyundai Motor Co. plant in the southeastern city of Ulsan on Tuesday, officials said. The three -- two Hyundai researchers and the other affiliated with a subcontractor -- were found collapsed at a test chamber of the plant where they were conducting a car performance test at around 3 p.m. in the day. According to Yonhap News Agency, they were taken to nearby hospitals but were pronounced dead, according to company officials and authorities. The victims were presumed to have been suffocated due to toxic gas in the enclosed space, and a police investigation is under way to find the exact cause of the accident.